Then you need copy file manually. In my OS (mint 20 cinnamon, opera 70) the command and paths are: $ sudo cp /snap/chromium-ffmpeg/15/chromium-ffmpeg-95241/chromium-ffmpeg/libffmpeg.so /usr/lib/x86_64-linux-gnu/opera/libffmpeg.so
Version 67 workrked fine for Facebook videos, version 68 does not Opera 54.
Youtube was not playing all videos. This solved!